1. The problem statement, all variables and given/known data 2. Relevant equations Power of a bulb = I2R = V2/R 3. The attempt at a solution From the ratings given on the bulbs using P=V2/R , we can conclude that resistances of the bulbs in decreasing order are R , P , Q i.e R has highest resistance and Q has lowest . Now brightness is related to power dissipated . Using P= I2R and the fact that both the current flowing in , as well as resistor of R is highest , so power dissipated in R should be highest . Now potential difference across P and Q is same and resistance of P is more than that of Q , so using V2/R , power dissipated in P should be lower . Hence least bright should be P . But R,P is not an option . What is the mistake ?